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BOC RAPTOR 200C & 250R MIG Operating manual
Welding Progression Angle
15.6 Fillet Welds
A fillet weld is approximately triangular in section, joining two
surfaces not in the same plane and forming a lap joint, tee joint or
corner joint. Joints made with fillet welds do not require extensive
edge preparation, as is the case with butt welded joints, since the
weld does not necessarily penetrate the full thickness of either
member. It is important that the parts to be joined be clean, close
fitting, and that all the edges on which welding is to be carried out
are square. On sheared plate it is advisable to entirely remove any
'false cut' on the edges prior to welding. Fillet welds are used in
the following types of joints:
'T' Joints
A fillet weld may be placed either on one or both sides,
depending on the requirements of the work. The weld metal
should fuse into or penetrate the corner formed between the
two members. Where possible the joint should be placed in
such a position as to form a "Natural 'V' fillet" since this is the
easiest and fastest method of fillet welding.
Lap Joints
In this case, a fillet weld may be placed either on one or
both sides of the joint, depending on accessibility and the
requirements of the joint. However, lap joints, where only
one weld is accessible, should be avoided where possible and
must never constitute the joints of tanks or other fabrications
where corrosion is likely to occur behind the lapped plates.
In applying fillet welds to lapped joints it is important that
the amount of overlap of the plates be not less than five
times the thickness of the thinner part. Where it is required to
preserve the outside face or contour of a structure, one plate
may be joggled.
Corner Joints
The members are fitted as shown, leaving a 'V'-shaped
groove in which a fillet weld is deposited. Fusion should be
complete for the full thickness of the metal. In practice it
is generally necessary to have a gap or a slight overlap on
the corner. The use of a 1.0–2.5 mm gap has the advantage
of assisting penetration at the root, although setting up is a
problem. The provision of an overlap largely overcomes the
problem of setting up, but prevents complete penetration
at the root and should therefore be kept to a minimum,
i.e. 1.0–2.5 mm.
The following terms and definitions are important in specifying and
describing fillet welds.
Leg Length
A fusion face of a fillet weld, as shown above. All specifications for
fillet weld sizes are based on leg length.
Throat Thickness
A measurement taken through the centre of a weld from the root
to the face, along the line that bisects the angle formed by the
members to be joined.
Effective throat thickness is a measurement on which the strength
of a weld is calculated. The effective throat thickness is based on a
mitre fillet (concave Fillet Weld), which has a throat thickness equal
to 70% of the leg length. For example, in the case of a 20 mm fillet,
the effective throat thickness will be 14 mm.
Convex Fillet Weld
A fillet weld in which the contour of the weld metal lies outside a
straight line joining the toes of the weld. A convex fillet weld of
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